The turbel- larian theory is also weak on embryological grounds, such as differences in cleavage patterns and germ layer formation. On development through alternating generations, especially in Coelenterata. For this reason, many authorities categorize Desor development as indirect (since a metamorphosis does occur), exemplifying one of the semantic problems of defining life cycle patterns. Booth Department of Biology Eastern Connecticut State University 83 Windham St.

For example, the tropical encrusting sponge Terpios grows over both living and nonliving substrata. As in all lophophorates, the digestive tract of ecto- procts is U-shaped (Figures 21.5, 21.9, 21.10, and 21.13). The slits open through pores on the exterior. It couldn't be easier to learn about everything from worms to wasps, as one book says in the title. Late in the spiral cleavage of certain animals, distinc- tive cell patterns appear, formed by the orientation of some of the apical first-quartet micromeres (Figure 4.5E).

Colony form is extremely variable, soft or calcified, encrusting to arborescent; body wall lacks muscles; zooids variably modified from basic cylindrical form; zooids usually polymorphic; lophophore circular, epistome and pro- tocoel absent; zooids joined by pores through which cords of tissue extend and join with each funiculus; two orders, Ctenos- tomata and Cheilostomata. Several studies have shown tardigrade sperm to be flagellated.

Figure 19.9 (A) A thread of the sticky spiral of an orb web with evenly distributed adhesive droplets. (B) Argiope on its orb web with a stabilimentum. (C) Funnel web of a funnel web spider (Dipluridae). (A) (B) (C) fpo slide here UNCORRECTED PAGE PROOFS ample, one idea is that silk was first used by supposed marine spiders to line and reinforce their mud burrows. Vol. 12, Onychophora, Chilopoda, and Lesser Proto- stomata. By using Latin names it allows for scientists in all countries to know what specimen they're discussing.

The choanocytes pump large volumes of water through the sponge body at very low pressures, establishing the water current (aquiferous) system. Our most important game and commercial fishes are represented in the Salmon Family. Giardia intestinalis, for example, will form a thick protective cov- ering that resists desiccation as it passes from the host’s small intestine into the large intestine, where it is prone to dehydration. Eventually the second meiotic division oc- curs, all but one of the nuclei disintegrate, and a haploid vegetative cell emerges from the cyst (Figure 5.28B). 152 CHAPTER FIVE Fusion of gametes Vegetative cell Dividing cell in gamete formation Gametes N 1N1N (Biflagellate) Motile 2N Motile 2N Zygote in resting stage Nonmotile Meiosis II Meiosis I Mitosis Figure 5.28 Phylum Dinoflagellata.

Nuclear division occurs by closed extranuclear pleuromitosis without centrioles 6. The appendages of such crustaceans are often broad and flattened, and they usu- ally bear fringes of setae that increase the effectiveness of the power stroke. Our mammal specimens have also played an integral role in such NMNH exhibitions as The Kenneth E. In the giant Pacific “gumboot” chiton, Cryptochiton stelleri, the girdle completely covers the valves. Abstract submission Offers of papers must be submitted by 26th February 1999.

In the 12 years since publication of Invertebrates, Second Edition, fundamental shifts have occurred in our understanding of the origins and evolutionary relationships among protists and animals. Adrianov, “Free-swimming Cellular Complexes in the Coelom of the Sipunculid Thysanocardia nigra Ikeda, 1904 (Sipuncula),” Russian Journal of Marine Biology, vol. 29, no. 3, pp. 180–184, 2003. The presumed primitive condition in polychaetes is a serially homonomous body with a pair of complete coelomic spaces in each segment.

It is important to offer a word of caution about the use of terminology among the various groups of arthro- pods. This behavior can eventually bring the animal near enough to the food source to home in on it directly. Our collections are badly in need of cleaning, conserving and remounting. On the prey-catching pedicellari- ae of a starfish, Stylasterias forreri. The classes Monogenea, Trematoda, and Cestoda share the unique synapomorphy of a tegument that arises during development through replacement of the larval epidermis by extensions of mesenchymal cells (1).

Hypothesis on the mechanism of cnidocyst discharge. Asexual reproduction by trans- verse fission and some anomalies in the sea anemone Nematostella vectensis. Choose two of the amphibians listed to look through and read through. The planula larva is radially symmetrical, but it swims with a dis- tinct “anterior– posterior” orientation. In terms of larval body orientation, the region between the mouth and anus apparently represents a much shortened dorsal surface and the “lower” side of the saclike trunk the ventral surface.